Justification:
This assessment is based on the information published in the 2005 shark status survey (Fowler et al. 2005).

This abundant pelagic and oceanic shark is widespread in temperate and tropical waters. It is relatively fast-growing and fecund, maturing in 4–6 years and producing average litters of 35 pups. The Blue Shark (Prionace glauca) is taken in large numbers (an estimated 20 million individuals annually), mainly as bycatch, but there are no population estimates and many catches are unreported. The few fishery assessments carried out suggest relatively little population decline. There is concern over the removal of such large numbers of this likely keystone predator from the oceanic ecosystem.

The Blue Shark is one of the most wide ranging of all sharks, being found throughout tropical and temperate seas from latitudes of about 60°N'50°S. It is oceanic and pelagic, found from the surface to about 350 m depth; occasionally it occurs close inshore where the continental shelf is narrow. The Blue Shark prefers temperatures of 12'20°C and is found at greater depths in tropical waters (Last and Stevens 1994).

The Blue Shark reaches a maximum size of about 380 cm TL. About 50% of males in the Atlantic are sexually mature by 218 cm, although some may reach maturity as small as 182 cm. Females are sub-adult from 173-221 cm and fully mature from 221 cm (Pratt 1979), although pregnant fish as small as 183 cm have been recorded from the eastern Pacific (Williams 1977).

Blue Sharks are placentally viviparous, producing litters averaging about 35 (maximum recorded 135) after a gestation period of 9-12 months. At birth the pups are 35-50 cm long. Reproduction has been reported as seasonal in most areas, with the young often born in spring or summer (Pratt 1979, Stevens 1984a, Nakano 1994) although the periods of ovulation and parturition may be extended (Strasburg 1958, Hazin et al. 1994). The skin of females is about three times thicker than that of males to withstand the extensive courtship bites of males. Females can store sperm in their nidamental glands for extended periods, for later fertilisation (Pratt 1979). Ageing studies suggest a longevity of about 20 years with males maturing at 4-6 and females at 5-7 years (Stevens 1975, Cailliet et al. 1983b, Nakano 1994). Smith et al. (1998) estimated the intrinsic rate of population increase at MSY to be 0.061.

Blue Sharks are highly migratory with complex movement patterns and spatial structure related to reproduction and the distribution of prey. There tends to be a seasonal shift in population abundance to higher latitudes associated with oceanic convergence or boundary zones as these are areas of higher productivity. Tagging studies of blue sharks have demonstrated extensive movements of blue sharks in the Atlantic with numerous trans-Atlantic migrations which are probably accomplished by swimming slowly and utilising the major current systems (Stevens 1976, Casey 1985, Stevens 1990). More limited tagging in the Pacific has also shown extensive movements of up to 9,200 km (P. Saul pers. comm.). Substantial data from the North Atlantic on the distribution, movements and reproductive behaviour of different segments of the population suggest a complex reproductive cycle. This involves major oceanic migrations associated with mating areas in the north-western Atlantic and pupping areas in the north-eastern Atlantic (Pratt 1979, Casey 1985, Stevens 1990).

The diet of Blue Sharks consists mainly of small pelagic fish and cephalopods, particularly squid; however, invertebrates (mainly pelagic crustaceans), small sharks, cetaceans (possibly carrion) and seabirds are also taken (Compagno 1984b). While most of the fish prey is pelagic, bottom fishes also feature in the diet. Blue sharks are known to feed throughout the 24-hour period but have been reported to be more active at night, with highest activity in the early evening (Sciarrotta and Nelson 1977).

Rarely a target commercial species, but a major bycatch of longline
and driftnet fisheries. Blue sharks are also
taken by sport fishermen. Periodically, small target fisheries have existed
for Blue Sharks.

Blue Sharks are rarely target commercial species but are a major bycatch of longline and driftnet fisheries, particularly from nations with high-seas fleets. Much of this bycatch is often unrecorded. Blue sharks are also taken by sport fishermen, particularly in the United States, Europe and Australia.

Periodically, small target fisheries have existed for Blue Sharks such as a seasonal longline fishery for juveniles of 50-150 cm near Vigo, Spain. Some 3t of gutted individuals were observed over a two-day period at Vigo fish market (A. Kingman pers. comm.). A Taiwanese (POC) longline fishery in Indonesian waters took about 13,000 t live weight of blue sharks in 1993 (N. Bentley pers. comm.).

Blue Shark catch rates reported from commercial longlining in the Atlantic Ocean range in average values from 2.9-100 (Stevens and Wayte 1999), while average catch rates as high as 145.0 have been recorded from research longlining (A. da Silva pers. comm.). Stevens (in press) estimated a catch of 137,800 t of Blue Shark from high-seas longline fleets, and 2,300 t from high-seas purse¬seining, in the Pacific in 1994. Bonfil (1994) calculated that 21,152 t of Blue Shark were taken by high-seas driftnet fleets in the Pacific during the 1989-90 period. The annual global catch of blue sharks is likely to be around 20 million individuals.

The limited fishery assessments carried out to date have shown no evidence of a declining trend in catch rates of Blue Sharks with time in the Atlantic or Indian Oceans. However, a 20% decrease was evident in the North Pacific between the periods 1971-1982 to 1983-1993 (Nakano 1996). No consistent decline in catch rates through the fishing season was evident for Japanese longliners fishing in Australian waters (Stevens and Wayte 1999).

The 1995 Fisheries Management Plan for pelagic sharks in Atlantic Canada established precautionary catch levels of 250 t for Blue Shark in the target shark fishery. License limitation, a ban on finning, restrictions on gear, area and seasons, bycatch limits and restrictions to recreational fishers permitting hook-and-release only were also implemented (Hurley 1998).

In 1991, Australia brought in legislation that prevented Japanese longliners fishing in the EEZ from landing shark fins unless they were accompanied by the carcass.

Since 1993, shark fisheries in Atlantic and Gulf of Mexico waters in the US have been managed under the Fishery Management Plan for Sharks of the Atlantic Ocean. The plan set commercial quotas for 10 species of pelagic sharks at 580t dressed weight annually, with recreational bag limits also applied. Commercial fishers require an annual shark permit, and finning is prohibited. In Mexico, a high-seas longline fishery taking pelagic sharks was banned within the EEZ in 1990 (Holts et al. 1998).

Holts, D.B., Julian, A., Sosa-Nishizaki, O. and Bartoo, N.W. 1998. Pelagic shark fisheries along the west coastof the United States and Baja California, Mexico. In: R.E. Hueter (ed.), Proceedings of an international symposium held at the 125th annual meeting of the American Fisheries Society, Tampa, Florida, USA, August 30, 1995, pp. 115–125.

Hurley, P.C.F. 1998. A review of the fishery for pelagic sharks in Atlantic Canada. Special issue science and management of shark fisheries. In: R.E. Hueter (ed.), Proceedings of an international symposium held at the 125th annual meeting of the American Fisheries Society, Tampa, Florida, USA, August 30, 1995, pp. 115–125.